Underdrilling roller bit



3 Sheets-Sheet 1 Filed Dec. 50, 1960 INVENTOR. James M. Cleory AltorneyATTEST M92? J. M. CLEARY UNDERDRILLING ROLLER BIT Dec. 1, 1964 FiledDec. 30, 1960 3 Sheets-Sheet 2 INVENTOR.

I James M. Cleory BYZ. jg-

Attorney Dec. 1, 1964 J. M. CLEARY 3,159,223

UNDERDRILLING ROLLER BIT Filed Dec. 50, 1960 s Sheets-Sheet 5 I I b Fig.7

AT TE S T INVEN TOR.

St I James M. Cleary Attorney United States Patent 3,159,223UNDERDRILLING BET James M. Clea, Dallas, Tern, assignor to The AtlanticRefining Company, Philadelphia, Pa, a corporation of Pennsylvania FiledDec. Sll, H56), Ser. No. 79,738 9 Claims. (Cl. 175-335) The presentinvention relates to an improved bit for drilling boreholes in theearth. In a more specific aspect, the present invention relates to animproved roller cone bit adapted to drill a borehole substantiallylarger than the bit itself. In one more specific form, the presentinvention relates to an improved roller cone bit adapted to straightenan inclined borehole.

In present-day operations for drilling boreholes in the earth,particularly for the production of oil and gas, a drill bit is suspendedfrom a tubular drill string and is rotated or rotated and vibrated whilea drilling fluid designed to remove cuttings from the hole is circulateddown the drill string across the bottom of the bit and back to thesurface of the earth. The vast majority of bits employed in present-daydrilling operations are capable of drilling a borehole no larger thanthe diameter of the bit itself.

' This fact causes many problems in drilling operations.

On occasion a buildup of cuttings or a combination of mud cake andcuttings on the sides of the hole wedge and stick the bit as it ispulled from the hole. This difficulty is most common in air or gasdrilling when a small amount of moisture is present in the hole.

It is also conventional in present-day operations to place casing in thehole after drilling has reached total depth. This casing is then used asa conduit for the production of fluids from the well and to controlcaving of incompetent formations and the production of unwanted fluids.Although the casing could be run while the hole is being drilled, thisis not practical since the normal drill bit drilling a holesubstantially larger than the internal diameter of the casing cannot beremoved or inserted through the casing. Accordingly, if casing is runduring drilling under these circumstances, the casing must be pulledeach time a bit is replaced. Since casing cannot be conveniently runduring the drilling operation, the walls of the formation are controlledby adding certain materials to the drilling fluid. Such additives arenecessary to seal the walls of the formation and prevent loss of theliquid portion of the drilling fiuid and prevent the caving ofincompetent formations. It is well known, however, that such additivesare detrimental to the main function of the drilling fluid since theyreduce drilling rate.

In addition, in recent years, gases, such as air have been employed asdrilling fluids. However, the use of gases to drill is often quitelimited because of, their failure to control and treat the walls of theborehole and the interference of formation fluids entering the borehole.The entry of fluids, such as water, into the borehole causes balling ofdrill cuttings and consequent interference with the drilling operation.In addition, if the hole cannot be cased as the drilling progresses, thehole may become partially filled with water or oil and gas drilling isthereby rendered impossible. Uncontrolled formation iluid production mayalso cause the blowout of such liquids at the surface.

Finally, due to discontinuities in the formations being penetrated,uneven wear of drilling bits, bending of the drill string and the like,boreholes often tend to drift from the vertical and become inclined.Since a very small ice deviation often becomes large, such deviation caneven result in the driller missing his target. It is, therefore,necessary to straighten the borehole periodically, which straighteningoperations interrupt normal drilling and are in themselves expensive.

It is, therefore, an object of the present invention to provide animproved roller cone bit combination.

It is another object of the present invention to provide an improvedroller cone bit adapted to drill a borehole substantially larger thanthe bit itself.

Itis a further object of the present invention to provide an improvedroller cone bit for underdrilling beneath a casing.

Still another object of the present invention is to pro vide an improvedroller cone bit which will permit casing of a borehole as drillingprogresses, which bit may be removed from the hole and reinsertedthrough the interior of the casing.

Mother and further object of the present invention is to provide animproved roller cone bit adapted to maintain a borehole vertical.

A still further object of the present invention is to provide animproved roller cone bit adapted to straighten an inclined borehole.

These and other objects of the present invention will become apparentfrom the following detailed description when read in conjunction withthe drawings.

In the drawings: I

FIGURE 1 is an elevational View, partially in section, of an improvedroller cone bit constructed in accordance with the present invention.

FIGURE 2 is a plan view of the bit of FIGURE 1.

FIGURE 3 is an elevational view, partially in section, of a furthermodification of the roller cone bit of the present invention. 7

FIGURE 4 is a plan View of the bit of FIGURE 3.

FIGURE 5 shows a third variation of the roller cone bit of the presentinvention.

FIGURE 6a is a plan view of the bit of FIGURE 5, and FIGURE 6b shows amodified pilot cutter of the bit of FIGURE 6a.

FIGURE 7 is a series of views showing the manner in which the bit of thepresent invention operates to enlarge a borehole.

FIGURE 8 is a series of views showing how the bit of the presentinvention may be utilized to straighten an inclined borehole.

The conventional roller cone bit usually includes a plurality of conesmounted on a bit body in a manner such that the cones will roll on asubstantially horizontal plane on the bottom of the borehole as the bitis rotated. These cones have mounted or formed thereon a plurality ofcutting teeth so that as the cone rolls these teeth chip or pulverizethe earth formation beneath the surface of the cone. Because of thenature and operation of the cutting teeth of the roller cone bit, thisbit is well suited for rotary percussive dnilling operations where thebit is both vertically vibrated and rotated. As previously indicated,such conventional roller cone bits drill a hole substantially the samesize as the bit itself and are thus subject to the same drawbacksexperienced in the use of other types of bits. However, it has beenfound in accordance with the present invention that a roller cone bitcan be constructed so that it will drill a borehole substantially largerin di ameter than the bit itself. This enlargement of a borehole isaccomplished in accordance with the present invention by mounting on oneside of the bit a pilot cutter whose axis of revolution is displacedfrom the central axis of the main bit and which is provided with anoncutting surface on the peripheral half or outer edge of the pilotmost remote from the axis of the main bit. This noncutting surface isadapted to cause the pilot to be 9 a forced in toward the center of thehole as drilling prograsses. Mounted on the opposite side of the bit andtrailing the pilot by a predetermined amount is a gage cutting rollercone adapted to cut an annular section of the formation immediatelysurrounding the pilot. As will be pointed out in more detail hereinafterthis bit reaches a stabilized position with the axis of the pilotcoincident with the central axis of the borehole and the gage cuttingroller sweeping around the pilot with the pilot axis as its axis ofrotation. It has further been found that if the cutter of the pilot isextended across the center of the pilot in the dire-ctiorrof thenoncutting surface, the subject bit may be employed to straighten aninclined well bore. 7

Referring in detail to FIGURES l and 2 of the drawings, there is shown amain bit body 1 which is threaded at its upper end 3 for attachment to aconventional drill string (not shown). If the bit is operated as arotary percussion bit the fluid motor is preferably mounted at 3immediately adjacent the bit. Mounted on one side of the bit body 1 isroller cone 5. The mounting of roller cone 5 is such that cone 5 willroll,'for example, on hearing 7, as the bit is rotated. Suitable teethare formed on the surface of cone 5 which cut into the formationbeneatih the cone as the bit is rotated and cone 5 rolls. As

"will be seen from FIGURE 1, center line of the main bit is midwaybetween the left side of bit body 1 and the gage cutting perimeter ofroller cone 5. Also mounted on bit body 1, generally opposite to rollercone 5, is roller cone '11. The central axis 13 of the pilot is betweenthe left side of bit body 1 and the apex of cone l1 and is offsct fromaxis 9 of the main-bit. Roller cone 11 is adapted to roll as the bit isrotated, as through bearing 15. Cone 11 leads cone 5 in the direction ofpenetration of the bit and, therefore, drills in advance of roller cone5. Ac-

cordingly, the bit maybe divided into gage cutting portion 17 and pilotcutting portion 19 as shown by the dashed horizontal line in FIGURE 1.This lead of roller cone 11 is extremely important to the operation ofthe bit as will be explained hereinafter. Formed on the peripheral halfor outer edge of pilot portion 19 most remote from axis 90f the main bitis a noncutti-ng surface 21 inclined inwardly and forwardly'withrelation to the downward direction of bit penetration. It will be seenthat inclined surface 21 extends beyond the perimeter of cutting teethon conell, as indicated by the small dashed circle of FIGURE 2.Noncutti-ng surface 21 causes pilot portion 19 to drift in toward thecenter of the borehole as drillingprogresses until axis 13 of the pilotis coincident Wit-h the central axis of the borehole, and the cutters onthe apex of cone 11 are cutting a pilot hole whose circumferenceincludes the furthermost extremity of noncurting surface 21. 'At thispoint it should be recognized that the cutters on the periphery of cone11 may be utilized to cut relief for noncutting surfaceZl rather thanthecutters on the apex of cone 11. In this case the angle of the conewould be larger than shown and cone 11 could have a frusto conicalshape. The bit becomes stabilized in this position; and cone 5 is thensweeping about the pilot hole with axis 13 of the pilot as its axis ofrotation and is, therefore, cutting the gage of a hole which issubstantially larger than the bit itself. The maximum size of the holeis shown by the'large dashed circle of FiG- URI-12. -It should be notedthat cones 5 and 11 may be inclined so that they do not roll on asubstantially horizontal plane as shown. However, if the bit is tobeemployed to maintain aborehole vertical or to straighten an inclinedborehole, the inclination of cones 5 and If.

should not be upwardly and outwardly by more than a .small angle. As isconventional in the construction and design of any bit, the bit is alsoprovided with drilling fluid channels 23 which supply drilling fluid tothe base of the bit. Finally, it should be recognized that more than onecone may be mounted on gage cutting portion 17 or on pilot portion 19 solong as the rollers on the pilot and in its final position.

the gage cutting portion are designed to function as previously setforth.

Referring now to FIGURES 3 and 4, it is to be recognized that numberscorresponding to those used in FIG- URES 1 and 2 have been utilized toindicate corresponding elements which perform substantially the same Wayto produce the same results. In FIGURES 3 and 4, roller cone 5 ismounted in substantially the same position and in the same way as is theroller cone on the bit of FIGURES 1 and 2. This cone will, therefore,cut the gage of the hole when the bit becomes stabilized However, inthis particular bit, the pilot portion has been modified by mounting adifferent type of cutting element thereon. Thus, pilot portion 19 hasmounted thereon a generally V-shaped per 19 most remote from centralaxis 9 of the bit pilot portion progresses.

19 and cutting element 25 have been inclined inwardly and forwardly withrelation to the direction of penetration of the bit. Thus, pilot portionf9 has formed thereon a noncutting surface 27 which will causepilotportion 19 to drift in toward the center of the borehole as drillingprogresses; ward the center axis 9 of the bit a sutficient distance sothat it will cut a pilot hole whose circumference includes thefurthermost extremity of noncutting surface 27. Thus, the cutter 25 willeventually cut relief for 'noncutting surface 27 when the pilot portion19 becomes cutting surface 27 is present and one of the cutters cutsrelief for noncutting surface 27. .In addition, a row or rows of spacedteeth or buttons may be substituted for the elongated cutter 25.

In still another modification of the present invention, as illustratedby FIGURES 5, 6a and 6b, the pilot portion 19 has mounted thereon adrag-type cutting blade 29; The bottom edge of cutting blade 29 isinclined upwardly and rearwardly with relation to the direction ofrotation of the bit so as to present a leading cutting edge which willbite into-the formation beneath the blade as drilling In theconfiguration shown, it is evident that the bottom of blade" 29 will bedragging tosome extent rather than cutting until the bit becomesstabilizcd. Thereafter, when the bit becomes stabilized, the innerportion of the bottom of blade 29 will be cutting and the outer portiondragging. This is not the most efiicient design. improved by splittingblade 29, sloping the inner portion as shown at 29 and reversing theslope of the outer portion as shown at 29' on FIGURE 6b. Formed on.

the outermost vertical edge of blade 2? is a noncutting surface '31.which is inclined inwardly and forwardly with relation to the directionof rotation of the bit. Because of the noncutting or dragging action ofsurface 31, pilot portion 19 drifts toward the center of the borehole asdrilling progresses. On the opposite side of pilot portion 19, cuttingsurface 33 is formed on blade 29. Cutting surface 33 is designedconventionally, sloping inwardly and rearwardly with relation to thedirection of rotation of the bit and, therefore, cuts into the walls ofthe pilot hole as the bit rotates. It should also be recognized thatcutting surface 33 is designed to de scribe a circle whose circumferenceincludes noncutting surface 31. Therefore, when the bit has becomestabilized with axis 13 of pilot portion 19 on the center line of thehole, cutting surface 33 will cut relief for noncutting surface 3d andthe bit will become stabilized since noncutting surface 31 can no longerforce the bit inwardly.

.In this stabilized position, the entire bit will rotate about Cutter 25extends inwardly to Accordingly, the cutting action can be axis 13 ofpilot portion 19 and roller cone 5 will cut an annular section offormation immediately surrounding the pilot hole. Therefore, this bitwill also drill a borehole substantially larger than the bit itself. Itis obvious that a plurality of drag-type cutting blades can be substituted for blade so long as noncutting surface 31 is present and oneof the blades cuts relief for surface 31 when the bit becomesstabilized. As will be explained later, it is the offset of the centeraxis 13 of pilot portion 19 from the center axis 9 of the main bit whichultimately determines the maximum diameter of the hole which will bedrilled.

As previously indicated, the distance by which pilot portion 19 leadsgage portion 17 is extremely important to the functioning of the bit inits intended manner. If the lead of the pilot is too small, the bit willfail to become stabilized due to the fact that the pilot hole is soshallow that the noncutting surface 31 will continuously destroy theshoulder of the pilot hole by lateral crushing and the bit will simplywobble about the hole rather than become stabilized. It has been foundthat the ratio of the lead of the pilot to the diameter of the main bitshould be at least'0.l5 in order to overcome this problem. The maximumlead of pilot portion 19 is an important design consideration since itshould be within certain limits which depends upon the strength of thepilot, the practical design of the connection at the upper end of thebit, etc. 7

FIGURE 7 of the drawings illustrates the manner in which the bit of thepresent invention enlarges a borehole. For this series of illustrations,a simplified version of the bit shown in FIGURES 1 and 2 is utilized.

View a of FIGURE 7 shows the bit disposed in a well bore having adiameter substantially equal to the diameter of the bit itself. Itshould be noted in View a that center axis 9 of the main bit iscoincident with central axis of the Well bore and that central axis 13of pilot portion 19 is offset from borehole axis 35. View b shows theconfiguration of the borehole after the bit has been operated for sometime. At this stage of the opera tion, noncutting surface 21 has forcedpilot portion 19 in toward the center of the borehole. As a result,central axis 9 of the main bit has moved off axis 35 of the borehole andis sweeping about the center axis of the borehole. By the same token,center axis 13 of pilot portion 19 has moved in toward center axis 35 ofthe borehole. At this stage, pilot roller cone 11 has begun to drill apilot hole equal to the depth of pilot portion 19 of the bit but stillsubstantially larger in diameter than pilot portion 19. Because of theshift of axes 9 and 13, gage roller cone 5 has begun to cut into thesides of the main borehole to thereby enlarge the hole somewhat. View 0shows another stage in the enlargement of the borehole after furtherpenetration of the bit. Because of the continued inward drift of pilotportion 19, axis 9 of the main bit has drifted further from axis 35 ofthe borehole and axis 13 of pilot portion 19 has drifted closer to axis35 of the borehole. As a result, the pilot hole has decreased indiameter by an amount equal to twice the shift of the axes and the gageof the main borehole has been enlarged by this same amount. Finally,View d shows the bit in its final stabilized position, in which positionit will contnue to drill a borehole substantially larger than thediameter of the bit itself. As shown in View d, axis 13 of pilot portion19 has drifted in toward axis 35 of the borehole until the two axes arecoincident. In addition, axis 9 of the main bit has drifted further fromaxis 35 of the borehole. Since the pilot hole is now substantially equalin diameter to the diameter of pilot portion 19 and pilot roller 11 isnow cutting a cylindrical pilot hole whose circumference includesnoncutting surface 21 of pilot portion 19, noncutting surface 21 nolonger forces the bit inwardly and the bit has become stabilized in theposition shown. The entire bit is now rotating about axis 13 of pilotportion 19. Consequently, gage cuttter 5 of gage t5 cutting portion 17is cutting an annular peripheral section of the hole immediatelysurroundingthe pilot hole.

By observing the operation as shown by FIGURE 7, it is obvious that theamount by which axis 13 of pilot portion 19 is offset from axis 9 of themain bit determines the amount by which the bit will enlarge the hole.Thus, the final diameter of the borehole is equal to twice the distancefrom axis 13 of pilot portion 19 to the outermost tip of gage cutter 5.Stated differently, the diameter of the borehole is larger than the bitdiameter by an amount equal to twice the distance from the center axis 9of the main bit to the center axis 13 of pilot portion 19.

FIGURE 8 shows a series of views illustrating the manner in which thebit of the present invention may be used to straighten an inclinedborehole. In View e of FIG- URE 8, the bit is shown positioned in aborehole larger than the diameter of the bit itself. This view is theequivalent of View d of FIGURE 7 except that the hole is inclined fromthe vertical. In order to straighten the subject hole, drilling isdiscontinued and the bit is lifted from the bottom of the hole. The bitis then dropped to the bottom of the hole and, due to gravity and theweight of the drill string supporting the bit, the bit will come to reston the low side of the hole. If pilot portion 19 strikes shoulder 37 onthe low side of the hole, the bit is then vibrated without rotation inorder to totally or partially destroy shoulder 37 as shown in View f.Having destroyed shoulder 37, rotation of the bit is resumed and the bitbegins to drill a new pilot hole closer to the original vertical axis ofthe hole. This is shown in View g of FIGURE 8. View g of FIGURE 8 showsthe condition of the hole after drilling has progressed to the stageshown in View 0 of FIGURE 7. At this stage, the bit has begun to drill apilot hole somewhat larger than the diameter of pilot portion 19 andgage cutting roller 5 has begun to cut into the low side of theborehole. View 71 then shows the bit after it has become stabilized inits new pilot hole and the new borehole. This condition is, of course,equivalent to that shown in View d of FIGURE 7 and View e of FIGURE 8except that the new pilot hole and the new main borehole are now closerto vertical than they are in View e of FIG- URE 8.

In order to completely return the borehole to vertical,

the above procedure may be repeated as many times as necessary. Inaddition, the borehole may be straightened intermittently as drillingprogresses without measuring the inclination of the hole or orientingthe bit so that pilot portion 19 will drop on shoulder 37. Obviously, ifthe straightening procedure is repeated a suflicient number of timesthroughout the progress of the drilling operation, pilot portion 19 willland on shoulder 37 a sufficient number of times to maintain theborehole vertical. On the other hand, if desired, the inclination of thehole may be measured at selected intervals and the bit properly orientedso that shoulder 37 will be wholly or partially destroyed by pilotportion 19 when the bit is dropped to the bottom and vibrated. Byselectively orienting the bit and following the above procedure it isalso possible to .start drilling an inclined hole at a diiferent angle.

There are several significant design features which must be present inthe bit in order to utilize it as a means for straightening a deviatedborehole. First, the cutters on the bottom of pilot portion 19 mustextend across axis 13 in the direction of noncutting surface 21. If thecutters do not extend beyond center line 13, the bit will not functionto destroy shoulder 37 but will simply slide off the shoulder and backinto the original pilot hole. For this same reason, the bottom of thecutters on pilot portion 19 should not be inclined upwardly andoutwardly by more than a small angle. If the pilot cutters are inclinedupwardly and outwardly by more than a small angle, the bit will againglance otf shoulder 37 and back into the original pilot hole rather thandestroy the shoulder and begin drilling a new pilot hole closer tovertical. Lastly, the

distance by which pilot portion 19 leads gage portion 17 should be asclose to the minimum as possible. In other words, the ratio of the leadof the pilot to the diameter of the bit should be greater than 0.15 butas close to that value as is practical. The ratio of the lead of thepilot to the diameter of the main bit may be expressed by the formula:

where R=ratio, x=length of pilot, and d =diameter of bit.

It is necessary that at least a part of shoulder 37 of FIG- URE 8 bedestroyed all the way to the bottom of the pilot hole if the bit is toform a new borehole axis shifted toward vertical. Otherwise, on renewingrotation of the. bit, the pilot would jump back into the remaining partof the pilot hole without shifting the axis of the borehole. In order todestroy shoulder 37 of FIGURE 8 by percussive action,

one must take into consideration the compressive sheer angle of theformation being drilled. The average sheer angle for most formationsencountered is about 28 degrees. Therefore, in order to destroy shoulder37 by percussive" action, the angle w of shoulder 37 (View e of FIGURE8) must be larger than about 28 degrees.

Observation of View 2 shows that angle w is related tothe diameter ofthebit, the diameter of pilot and the length of the pilot. The followingexpression can, therefore, be written:

tan in= d1 where d diameter of the pilot.

Then: 7 I

' (1 -61, tan w and since,

i a: B it then can to For example, in the bits shown in the drawings, wis 65 degrees and R==0.233.

. modifications and variations may be made without departing from thepresent invention. Accordingly, the present invention is limited only inaccordance with-the appended claims.

I claim:

1. An irnprovedbit for drilling a borehole in the earth comprising amain bit body, rotary pilot drilling means on said bit'body whose axisof revolution is offset from the central axis of said bit body, asloping noncutting surface on the outer edge of said pilot drillingmeans most rem'otefrom said axis of said bit body and adapted to forcesaid pilot drilling means. inwardly as drilling progresses, rotarycutting means on said pilot drilling means adapted to drill a pilot holewhose circumference includes the outermost extremity of said noncuttingsurface when said axis of said pilot drilling means coincides with thecentral axis of said borehole and at least one first roller cone cuttingmeans mounted on said bit body above said rotary cutting means on saidpilot drilling means with respect to the direction of penetration ofsaid bit, said first roller cone cutting means adapted to drill anannular section of the earth immediately surrounding said pilot hole andtrailing said pilot hole with respect to the direction of penetration ofsaid bit and the outermost tip of the cutting edges of said pilotdrilling means at the bottom of said pilot hole leading the lowermostcutting edges of said at least one first roller cone cutting means by adistance sufficient to stabilize said bit in said borehole when saidaxis of said pilot drilling means coincides with the central axis ofsaid borehole.

2. A bit in accordance with claim 1 wherein the rotary cutting means onthe pilot drilling means includes at least one drag-type blade.

3. A bit in accordance with claim 2 wherein the outermost tips of thecutting edges of the pilot drilling means at the bottom of thewalls ofthe pilot hole lead the lower most cutting edges of the at least onefirst roller cone cutting means by a distance between 0.15 and 1.25times the maximum width of the bit. I

4. A bit in accordance with claim 3 wherein the noncutting surface isformed on the drag-type blade and slopes inwardly and forwardly withrelation to the direction of rotation of the bit.

5. A bit in accordance with claim 1 wherein the bit is adapted to drillby rotary percussive action and the rotary cutting means on the pilotdrilling means has a cutting edge extending across substantially theentire pilot in the direciton of the noncutting surface.

6. A bit in accordance with claim 1 wherein the cutting means on thepilot drilling means is at least one second roller cone cutting meansset inwardly from the momentting surface toward the center of the bitbody.

7. A bit in accordance with'claim 6 wherein the outermost tips of thecutting edges of the pilot drilling means at the bottom of the walls ofthe pilot hole lead the lowermost cutting edges of the at least onefirst roller cone cutting means by a distance between 0.15 and 1.25times the maximum width of the bit.

8. A bit in accordance with claim 7 wherein the noncutting surface,formed on the pilot drilling means slopes adapted to drill by rotarypercussive action and the rotary cutting means on the pilot drillingmeans has a cutting edge extending laterally beyond the axis of saidpilot 'means in the direction of the noncutting surface.

References Cited in thefile of this patent UNITED STATES PATENTS GermanyFeb. 28, 1929 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent N0. 3, 159,223 December 1, 19641 James M. Glear'y It i h b 'bii'irequiijinfg t rgz ign 75,3 3? or @PPQZTF lbD/ln quimmi; t; lii ixxs mtgfi M s-aawcd s.

int: \B {or he" second occurrgsnce, reaa ec fi iii 29, sex-1k out "the":aolumn 5, l1ne 26, for depend 5 read depend sama column 5, l ne 63, for

"contnue" read continue Signed and Gfild this 20th day of April 1965.

(SEAL) Auest:

ERNEST W. SWIDER' EDWARD J. BRENNER Alwfiling Office! Commissioner ofPatents

1. AN IMPROVED BIT FOR DRILLING A BOREHOLE IN THE EARTH COMPRISING A MAIN BIT BODY, ROTARY PILOT DRILLING MEANS ON SAID BIT BODY WHOSE AXIS OF REVOLUTION IS OFFSET FROM THE CENTRAL AXIS OF SAID BIT BODY, A SLOPING NONCUTTING SURFACE ON THE OUTER EDGE OF SAID PILOT DRILLING MEANS MOST REMOTE FROM SAID AXIS OF SAID BIT BODY AND ADAPTED TO FORCE SAID PILOT DRILLING MEANS INWARDLY AS DRILLING PROGRESSES, ROTARY CUTTING MEANS ON SAID PILOT DRILLING MEANS ADAPTED TO DRILL A PILOT HOLE WHOSE CIRCUMFERENCE INCLUDES THE OUTERMOST EXTREMITY OF SAID NONCUTTING SURFACE WHEN SAID AXIS OF SAID PILOT DRILLING MEANS COINCIDES WITH THE CENTRAL AXIS OF SAID BOREHOLE AND AT LEAST ONE FIRST ROLLER CONE CUTTING MEANS MOUNTED ON SAID BIT BODY ABOVE SAID ROTARY CUTTING MEANS ON SAID PILOT DRILLING MEANS WITH RESPECT TO THE DIRECTION OF PENETRATION OF SAID BIT, SAID FIRST ROLLER CONE CUTTING MEANS ADAPTED TO DRILL AN ANNULAR SECTION OF THE EARTH IMMEDIATELY SURROUNDING SAID PILOT HOLE AND TRAILING SAID PILOT HOLE WITH RESPECT TO THE DIRECTION OF PENETRATION OF SAID BIT AND THE OUTERMOST TIP OF THE CUTTING EDGES OF SAID PILOT DRILLING MEANS AT THE BOTTOM OF SAID PILOT HOLE LEADING THE LOWERMOST CUTTING EDGES OF SAID AT LEAST ONE FIRST ROLLER CONE CUTTING MEANS BY A DISTANCE SUFFICIENT TO STABILIZE SAID BIT IN SAID BOREHOLE WHEN SAID AXIS OF SAID PILOT DRILLING MEANS COINCIDES WITH THE CENTRAL AXIS OF SAID BOREHOLE. 